1. Field of the Invention
The present invention relates to a piezoelectric ceramic transformer, in particular, to a non-symmetric drive type piezoelectric ceramic transformer, which has simply formation process, high boosting ratio, high conversion efficiency, adjustable resonance frequency and oscillation node. The present invention belongs to the electronic technique.
2. Description of Related Art
At present, there are two kinds of common piezoelectric ceramic transformer, i.e. Rosen type piezoelectric ceramic transformer and Center type piezoelectric ceramic transformer.
As shown in FIGS. 1 and 2, Rosen type piezoelectric ceramic transformer is a rectangular piezoelectric which is divided into two half-zones, the left zone 1 is called as input drive zone, the both surface of which are coated with electrodes 11 and is polarized along its thickness; the right zone 2 is called as output generation zone, the end of which is coated with electrode 21, and is polarized along its length. This structure of Rosen type piezoelectric ceramic transformer has mainly two oscillation modes, λ/2 and λ. In practical applications, the higher the resonance frequency of a transformer, the greater the loss is, so that the piezoelectric ceramic transformer is usually operated in oscillation mode λ/2. When it is operating on oscillation mode λ/2, the null displacement oscillation node is at the center of the transformer, the oscillation displacement of output head of the right zone 2 is equal to that of the left zone 1, the oscillating displacement diagram is a symmetric diagram. The advantage of Rosen type piezoelectric ceramic transformer is simple in manufacturing engineering. Its advantage is as follows: high manufacturing cost resulting from large electrode areas of input drive zone, large input capacitance, large phase, low boosting ratio, low conversion efficiency and unadjustable resonance frequency and oscillation node.
As shown in FIGS. 3 and 4, the Center type piezoelectric ceramic transformer is a rectangular piezoelectric, which is divided into three zones: the middle zone 3 is an input drive zone, the upper and lower surface of which is coated with electrode 31, and which is polarized along its thickness; the both side of which is output generation zone 4 and 5, each head is coated with electrode 41, 51, and which is polarized along their length, the both output generation zone is symmetrical and has the same phase. In practical application they are joining-up in parallel. The Center type piezoelectric ceramic transformer mainly has two oscillation modes, i.e., λ/2 and 3λ/2. When it is operated on oscillation mode λ/2, the null displacement oscillation node is at the center of the transformer, the oscillating displacement of both output head is equal, and the oscillating displacement diagram is the diagram of symmetry type. The advantage of Center type piezoelectric ceramic transformer is high boosting ratio, while the disadvantage is as follows: complex manufacturing engineering, high manufacturing cost, high requirements for balancing degree of the two generation zones, modulation phenomena resulting from the addition of waveforms when joining-up in parallel, and unadjustable resonance frequency and oscillation node.